The diameter of silicon single crystals manufactured by using the Czochralski method (CZ method) has been increasing in recent years. In order to grow a large diameter crystal, a large amount, 100 kg or more, of the source material has to be melted using a large diameter quartz crucible. However, there may be a problem in the crystal quality. In order to obtain a quality crystal, the concentration of the interstitial oxygen contained in the crystal has to be low. However, the oxygen contained in the crystal is supplied by dissolution of the quartz crucible. Therefore, the oxygen supplied from the quartz crucible increases, resulting in an increase in the interstitial oxygen, as the quartz crucible becomes larger and the amount of the silicon melt increases.
In addition, when growing a crystal with a larger diameter, the increased amount of the melt increases the instability of the melt due to natural convection, making it harder to grow the crystal.
The MCZ method has been used as a method to solve the aforementioned problem. In the MCZ method, the melt convection and the introduction of oxygen dissolved in the melt into the crystal can be controlled by applying a magnetic field when pulling the crystal.
However, when a crystal with a large diameter is pulled with the MCZ method, a new problem arises in that the crystal becomes distorted. This distortion of the crystal happens more easily when the crystal rotation speed is increased. Once a twist occurs, the crystal is deformed and tends to lose the single crystal quality. When the crystal is distorted, the crystal growth rate has to be reduced and therefore there is a problem in that the manufacturing efficiency decreases, resulting in higher costs.
Therefore, in order to orvercome the problem of distortion, it is necessary to reduce the crystal rotation speed. However, the crystal rotation speed is an important growth parameter for obtaining a homogeneous distribution of the impurity in the obtained wafer, and problems will arise if the crystal rotation speed is reduced below a certain point.
Therefore, the object of the present invention is to provide a method of manufacturing a silicon single crystal with a large diameter using the MCZ method without causing distortion.